This invention relates to devices for converting linear motion into rotatory motion and vice versa, and is particularly, although not exclusively, applicable to pressure fluid operated devices, for example, pneumatic and hydraulic actuators, air motors, and pumps.
One type of device to which the invention is particularly applicable is a pneumatic or hydraulic actuator for a quarter-turn valve, for example, a plug valve. Such an actuator is required to convert the generally linear force or motion produced by a piston in a pneumatic or hydraulic cylinder into a torque or rotatory motion applied to the operating shaft of the valve. Commonly, a 90 degree rotation of the operating shaft is required to open and close the valve. Existing devices for converting the linear motion of the piston into the required rotatory motion are somewhat cumbersome and expensive, a common form of such device using a rack-and-pinion mechanism.